Fast Switching VSG Fits In PXIe Format

Measurement systems at one time implied heavy racks of equipment. But a growing number of high-frequency test functions are now available in such modular formats as PXI and PXIe, making it possible to shave size.

Measurement systems at one time implied heavy 19-in.-wide racks of equipment, each with its own power supply and set of controls. But a growing number of high-frequency test functions are now available in such modular formats as PXI and PXIe, making it possible to assembly a complete RF/microwave test system by sliding compact instrument modules into a card chassis. The M9381A PXIe vector signal generator from Agilent Technologies (www.agilent.com) is one example of how far this format has come.

Available to create stable vector-modulated [with in-phase (I) and quadrature (Q) components] signals from 1 MHz to either 3 GHz or 6 GHz, the M9381A VSG occupies only five slots in a PXIe chassis (many of which can hold 18 slots and still mount in a 19-in. rack). It takes full advantage of the speed PXIe backplane to achieve some of the fastest VSG frequency and amplitude switching speed in the industry, greatly accelerating the pace of automated-test-equipment (ATE) production-line measurements.

Those five PXIe slots for the M9381A (see figure) include a model M9300A frequency reference module (one slot), the M9301A PXIe synthesizer module (one slot), the M9310A PXIe source output module (one slot), and the M9311A PXIe digital vector modulator (two slots). With the appropriate software drivers and test software running on a PXIe controller or on an external computer connected to the PXIe chassis, the M931A can be fully controlled, with all functions shown on the computer screen along with waveform displays. The computer or controller in a PXIe setup essentially takes the place of the front-panel controls and display screen on a conventional benchtop, rack-mount type RF/microwave instrument (such as a VSG).

The M9381A is available in various versions, with a base configuration (model M9381A-F03) that has a 40-MHz modulation bandwidth across a frequency range of 1 MHz to 3 GHz. It is supported by 32 MSamples of waveform memory. The frequency range can be extended to 6 GHz (model M9381A-F06), the modulation bandwidth to 100 or 160 MHz, and the sample memory to 512 or 1024 MSamples. Across the 40-MHz modulation bandwidth, the typical amplitude flatness is ±0.2 dB, with ±0.3-dB typical flatness across the 100-MHz modulation bandwidth and ±0.5-dB typical flatness across the 160-MHz modulation bandwidth. The M9381A can generate a variety of modulation formats over those bandwidths, including amplitude modulation (AM), frequency modulation (FM), pulse modulation, and multitone modulation. In either the 3- or 6-GHz model, the frequency tuning resolution is a fine 0.01 Hz.

The M9381A VSG uses a list-mode function to execute rapid changes in frequency and amplitude, as might be needed for production-line testing of mobile or wireless communications devices. A standard model M9381A switches frequency and amplitude in about 5 ms. A high-speed option (UNZ) reduces this time to only 2 ms. When the list-mode feature is used in a standard model M9381A, the switching speed is still typically 5 ms, but with a model M9381A equipped with option UNZ, changes in frequency and amplitude can be made in only 220 μs and changes in amplitude in only 125 μs.

The list mode allows as many as 80 channel parameters to be set for each switched mode, including frequency and power. The M9381A also provides baseband tuning capability driven by a custom application-specific integrated circuit (ASIC). It allows for high-speed changes within ±80 MHz of a carrier frequency, or from 0 to -20 dB from an RF power level. In a standard model M9381A, the baseband tuning speed is about 5 ms. With option UNZ, the baseband tuning speed is typically 250 μs in response to commands from a controller or computer and typically only 10 μs with the list-mode function.

Output power on a standard model M9381A can be set from -130 to +10.7 dBm with 0.3-dB typical resolution. The VSG also features a highly accurate automatic-level-control (ALC) function based on precision step attenuators that provides 0.02-dB power-level resolution when engaged. The maximum output power in the standard model M9381A is +10 dBm through either 3 or 6 GHz. With option 1EA, as much as +19-dBm output power is available to 2.5 GHz and as much as +18-dBm power to 6 GHz.

The M9381A has a stable reference module (model M9300A) based on a 10-MHz oven-controlled crystal oscillator and 100-MHz phase-locked loop (PLL). It provides reference signals of 10 MHz at +9.5 dBm and 100 MHz at +10 dBm, with daily aging rate of better than ±0.5 ppb/day after a 72-hour warmup period and a yearly aging rate of better than ±0.10 ppm/year after a 72-hour warmup period. The reference module can also work with external sinewave signals from 10 to 110 MHz at levels of 0 to +10 dBm when even higher precision is required. With its M9300A reference module, the M9381A VSG exhibits phase noise of -122 dBc/Hz offset 20 kHz from a 1-GHz carrier and -108 dBc/Hz offset 20 kHz from a 6-GHz carrier. Harmonics are typically -30 dBc or better, while spurious levels are -70 dBc or better.

The M9381A is supplied with a CD containing product information, sample programs, drivers, and software, including Agilent’s Signal Studio signal creation software. Signal Studio provides validated and performance-optimized reference signals for cellular and wireless connectivity standards in an easy-to-use, application-specific graphical interface. The PXIe VSG supports interfaces for VisualStudio from Microsoft (www.microsoft.com), MATLAB from MathWorks (www.mathworks.com), and LabVIEW from National Instruments (www.ni.com). The VSG is also supported by Agilent’s N7800A calibration software which checks that modules meet specified performance levels and helps users manage their calibration intervals. P&A: $25,663 and up (3-GHz version).